import java.util.*;


//已知两颗二叉树，将它们合并成一颗二叉树。
// 合并规则是：都存在的结点，就将结点值加起来，否则空的位置就由另一个树的结点来代替。
public class Solution {
    public class TreeNode {
        int val = 0;
        TreeNode left = null;
        TreeNode right = null;
        public TreeNode(int val) {
            this.val = val;
        }
    }

    public TreeNode mergeTrees (TreeNode t1, TreeNode t2) {
        if (t1 == null) {
            return t2;
        }
        if (t2 == null) {
            return t1;
        }
        TreeNode newRoot = new TreeNode(t1.val+t2.val);
        newRoot.left = mergeTrees(t1.left,t2.left);
        newRoot.right = mergeTrees(t1.right,t2.right);
        return newRoot;
    }



}